The present invention relates to a method for manufacturing diodes. A previously proposed diode manufacturing method is described in German Published Patent Application No. 43 20 780, in which doping films are used.
In contrast, the method according to the present invention has the advantage that flatter doping profiles can be generated, in which the surface concentration can be at a lower level. As a result of the fact that it is possible to generate a flat outflow of the doping concentration into the depths of the wafer, the forward voltage of the diode is lower. Similarly, the avalanche voltage at high current flows, e.g. 100 A, is made significantly smaller, i.e., the path resistance in the diode is reduced. In addition, the diode is easier to manufacture because the Zener voltage of the diode is less sensitive to certain fluctuations in response to a second diffusion in a series production, in which the actual p-n junction is produced. As a result of the fact that it is possible to produce a low surface concentration, while at the same time maintaining a deep outflow of the doping concentration, it is possible to carry out a second diffusion, in which the pn junction is produced, using a doping film that is doped at a lower level. In this manner, the Zener voltage in series production can be xe2x80x9cmetxe2x80x9d or maintained without taking special precautions. As a result of a second doping that can be weaker, the surface of the silicon wafer is also not so intensively concentrated in impurities, so that the silicon crystal lattice is not disturbed, and therefore bending the wafer is avoided. It is additionally advantageous that the neutral film used also functions as protection during a further driving-in. The neutral film is placed onto an already doped silicon surface and, when doping atoms are once again driven in, it reliably prevents contamination of the surface, without any additional surface covering.
It is particularly advantageous to cover the upper side of the wafer using a neutral film in a second partial step, the lower side of the wafer being covered using a doping film for a very strong doping. In this manner, it is possible, on the one hand, to obtain a deep doping profile, and on the other hand, to simultaneously dope the lower side of the wafer more strongly in order to make possible an effective backside bonding of the diode.
The further application of a doping film of the opposite conductivity type makes possible a simple and also error-tolerant production of the pn junction of the diode.